In modern medical practice, it is common to infuse more than one medicating liquid into a patient at the same or nearly the same time. For this purpose, multi-lumen IV infusion devices are frequently used so that a single patient infusion site may be employed. Most multi-lumen systems are of the type wherein the multiple lumen feature is incorporated within the intravascular catheter itself, and are usually used for more invasive IV approaches as subclavian, internal jugular, or for venous access via a cut down procedure. Some existing multiple lumen IV devices require an entire IV system to be set up for each of the infusion channels being used. The set up includes an IV fluid bag, the IV administration tubing set, and, if extra length is desired, an extension set for each channel as well.
One system, available from Abbott Laboratories, Inc., does allow a two channel infusion into one venipuncture, with the double channel being external to the patient. However, the Abbott system requires a duplicate set of fluid bags, administration sets, and extension tubing.
One method of infusing of a plurality of medications externally into a single lumen catheter is through the use of an extension set. Use of various kinds of extension sets are known in the art. Extension sets are available in the art for continuous and intermittent delivery of medications through an IV tube to an indwelling patient catheter. For such purposes, "Y" connections are provided at an upstream site in the extension set where injection is made. Often a hypodermic syringe is used to pierce a self-sealing diaphragm at the end of one branch of the "Y" connection to introduce a medication into a single orifice extending tube of the extension set.
A significant problem of introducing such medications at an upstream site to flow therefrom to an indwellng infusion catheter through such a single orifice tube is mixing which occurs with other fluids resident in the tube and a resultant dilution of the medicant which occurs prior to reaching the indwelling patient catheter. Such mixing and dilution changes the time course and concentration of the administered drug and the ensuing patient response.
Some IV infused drugs are powerful in very small amounts, such as Nitroglycerine, Nitroprusside, Xylocaine, Dopamine, and Isuprel. During administration of such drugs, it often becomes necessary to rapidly slow down or quickly halt the drug infusion rate due to an exaggerated response of the patient. In IV tubing systems where there is any upstream mixing, all infusion must be stopped entirely to quickly halt the drug infusion. A common complication of stopping all IV flow is clotting which can result in a lost IV infusion site. Recovery of the IV infusion site raises the risk that a new IV bottle and administration set may be used, but the same extension set may be retained whereupon the new IV fluid is "flushed in" through the extension set containing a portion of the drug previously stopped. The previously stopped drug is then flushed through to cause an undesired patient response.
An example of a drug administered by IV which requires a precise titration to a patient is IV Dopamine, a commonly given IV medication for hypotension. The administration of Dopamine is often complicated by a need to rapidly infuse a large volume of fluid concurrent with the Dopamine infusion to augment blood pressure.
The above cited examples of problems associated with very potent medications demonstrate the need for carefully controlling administration rates and delivering some medications separately from other IV infused liquids. For these purposes and to provide a haltable medication delivery pathway, a dual lumen extension set having one smaller lumen and one larger lumen is used. Such medication is normally delivered through the smaller lumen while the larger lumen is used to maintain a second, and perhaps greater, liquid infusion rate.
One of the major problems associated with infusion of drugs into extension sets upstream from an indwelling catheter is dead space. Dead space may be considered to be of two types, geometric and dynamic. Geometric dead space is defined as the space within a device which is not functionally useful, such as a portion of the space within a device which receives a bolus of liquid but from which the share of liquid received by the dead space does not evacuate immediately when the rest of the liquid is washed therefrom. Most often liquid captured in a geometric dead space washes out over a relatively long period of time thereby diluting and distorting the downstream effect of the liquid medication injected as a single bolus into the device. Dynamic dead space is defined as space which is completely cleared by a single wash, but only after a primary injecting function is completed and a subsequent clearing wash function is later performed. Any delay in performing the clearing function also distorts the downstream effect of an injected bolus of medication.
Clinicians frequently increase a cleansing flow of saline or other high volume wash fluid through a known geometric dead space containing device to a "wide open" state for a brief period to wash out the liquid retained in the geometric dead space. Such a "wide open" state of flow into any indwelling catheter is potentially hazardous if left open for too long a time. Bedside processes involved in correcting for inherent geometric dead space are therefore both detrimental to efficiently providing patient IV care and, in some circumstances, life threatening.
A proposed solution to the problems of geometric dead space and dilution of an administered medication through an extension set is advanced in U.S. Pat. No. 4,585,435 which discloses a dual lumen extension tube and a "Y" connection wherein a bolus of medication is delivered by a syringe needle inserted through a sealable membrane into one lumen of the extension tube which is described as being substantially smaller than the other lumen. Flow from both lumens is delivered to a common distal site near the influent port of the patient catheter.
While the medication is sent through the smaller lumen of the extension tube toward the influent port of the patient catheter in a substantially undiluted state, a significant portion of the injected liquid medication remains upstream in the smaller lumen at the end of the syringe needle injection. In order for the total bolus of medication to be delivered to the indwelling patient catheter, an injection of wash liquid must be delivered by a second injection procedure. This second procedure may be time consuming and involve an undesirably delay.
As a result, delivery of the total medication is provided in two discreet time periods. A first partial bolus of the medication is delivered to the patient substantially simultaneously with the syringe injection. Later, a second remaining bolus of medication is delivered at a time dependent upon the speed and dexterity of the technician in removing the syringe and injecting a wash solution with a second syringe. Thus, even though a very small geometric dead space is inherent in the smaller lumen, the delay in washing out the second remaining bolus appears as a dynamic dead space in the delivery of the total medication to the patient.